laser tools - which one?

Mary needs some good advice. Here is the problem:

Can i get tips on laser tools ? i am interested in using a laser to construct a wall to divide a room. i borrowed a friends laser (black and decker bdl310s, $80 at hd) and got very frustrated trying to make the outline of the wall on the two walls and ceiling and floor. i ended up, to determine how to get the new wall square to the room, measuring off an existing wall onto 2points on the ceiling, dropping a point onto the floor w/ a plumb line from those two ceiling points, and only using the laser from this point on to extend those 4points into a square outline. i was really expecting the laser to help eliminate the plumb line and the 'measuring off the wall' step.

could it have been easier ? what laser product can anyone recommend ? very frustrating.